The invention relates generally to ultrasound systems and more specifically to transmit/receive circuitry in ultrasound systems.
An ultrasound imaging system forms an image by acquiring individual ultrasound lines (or beams). Conventional ultrasound imaging systems comprise an array of ultrasonic transducer elements that are used to transmit an ultrasound beam and then receive the reflected beam from the object being studied. Such scanning comprises a series of measurements in which the focused ultrasonic wave is transmitted, the system switches to receive mode after a short time interval, and the reflected ultrasonic wave is received, beamformed and processed for display.
For ultrasound imaging, the array typically has a multiplicity of transducer elements arranged in one or more rows and driven with separate voltages. By selecting the time delay (or phase) and amplitude of the applied voltages, the individual transducer elements in a given row can be controlled to produce ultrasonic waves that combine to form a net ultrasonic wave that travels along a preferred vector direction and is focused in a selected zone along the beam.
The same principles apply when the transducer probe is employed to receive the reflected sound in a receive mode. The voltages produced at the receiving transducer elements are summed so that the net signal is indicative of the ultrasound reflected from a single focal zone in the object. As with the transmission mode, this focused reception of the ultrasonic energy is achieved by imparting separate time delay (and/or phase shifts) and gains to the signal from each receiving transducer element.
The ultrasonic transducer elements are typically located in a hand-held transducer probe that is connected by a flexible cable to an electronics unit that processes the transducer signals and generates ultrasound images. The transducer probe may also carry ultrasound transmit and receive circuitry.
The transmit circuitry usually includes high-voltage components, which are used to drive the individual ultrasonic transducer elements, and low-voltage, high-density digital logic circuitry used to provide transmit signals to the high-voltage drivers. The high-voltage drivers typically operate at voltages of up to approximately ±100 volts, while the low-voltage logic circuitry has an operating voltage on the order of 5 volts in the case of Transistor Transistor Logic (TTL). The high-voltage drivers may be fabricated as discrete components or as integrated circuits, while the low-voltage logic circuitry may be fabricated as a separate integrated circuit or combined with the high-voltage circuitry on a single chip.
In addition to transmit circuitry including the high-voltage drivers and low-voltage logic circuitry, the transducer head may include low-noise, low-voltage analog receive circuitry. The low-voltage receive circuitry, like the transmit logic circuitry, typically has an operating voltage on the order of 5 volts, and may be a separate integrated circuit or may be fabricated with the low-voltage transmit logic circuitry as a monolithic integrated circuit.
The transmit/receive circuitry has two states. In the transmit state, the transmit/receive circuitry connects the output-stage transistors to the ultrasonic transducer element, while isolating the receive circuit from the high-voltage transmit pulse. In the receive state, the transmit/receive circuitry isolates the output-stage transistors from the ultrasonic transducer element and instead connects the receive circuit to the transducer element.
In most ultrasound imaging systems, the transmit/receive circuitry is disposed in the system while the transducer elements are disposed on the ultrasound probe. For greater integration, it is advantageous to dispose the transmitter circuitry and/or the receive circuitry in the probe also. The presence of high voltage components results in larger area required by the transmit/receive circuitry. To accommodate the transmit/receive circuitry into the probe, it is often required to reduce the number of processing channels. However, reducing the number of processing channels will lead to degradation in the image quality.
Therefore, what is needed is low-cost compact transmit/receive circuitry while maintaining image quality.